Heat treatment for aluminum base alloys



' con, magnesium and copper. heat treatmentv applied to alloys consisting of Pate med June 11, 1041 UNITED- STATES PATENT OFFICE HEAT, TREATMENT FOR ALUMINUM BASE ALLOYS Richards H. Harrington, Schenectady, N. Y., assignor to'General Electric Compa y, a corporation of New York No Drawing. Application July 29, 1938,

Serial No. 221,97

2 Claims. (01. 148-211) The present invention relates to heat treatment for aluminum base alloys andmore particularly to a heat treatment for aluminum alloys containing more than 90% aluminum with the remaindereither silicon and magnesium, or sili- -aluminum,' silicon and magnesium comprised heating the castings for approximately twelve hours at 538 C. to eflect a solution condition inthe alloy, quenching, and reheating for about three to live hours at 160 C. to effect a condition of precipitation. -The properties resulting from the application of such a heat treatment to castings consisting of 7% silicon, 0.3% magnesium andthe remainder aluminum are substantlally as follows:

Proportional limit v 1 pounds per square inch 12,000

iem strength -do 22,000 .Tenslle strength do.. 31,000 Elongation;.. e es per cent 3to4 1 It isone of the objects of the present invention Proportional limit lbs. per sq. in 20,000 to 24,000

Yield strength do.. 28,000 Tensile strength "do--- 37,000 to 40,000 Elongation per cent- 3 to 4- Numerous tests have indicated that the solution temperature and the time the alloy is held at that temperature are critical. Any deviation from the solution temperature greater than plus or Heretofore theminus 5 C. results for example in greatly lowered tensile properties in the alloy. Furthermore, any

I leads to grain growth whichis harmful. Also, the time should be as short as possible to reduce warping. The precipitation reheat temperature of 155 C, and the time at tbat'temperature are also somewhat critical but small deviatiom in reheat temperature are not harmful to the same degree as in the solutiontemperature. For ex,- amplevariations of C. in the reheat temperaturedo not result in a serious loss of properties in the alloy. A reheat. period of less than ten hours tends to lower the elongation to about 2% while a period greater than twenty hours effects no practical improvement,

While I prefer to employ an alloy having the above noted composition, my method is not restricted to that specific composition but may be i applied to aluminum base alloys containing silicon, magnesium and copper. Alloys of this latter composition heretofore have been heat treated to improve their physical properties, the heat treatment comprising heating for twenty hours,

at 520 C., quenching in water and reheating four hours at 0. Such a heat treatment does not develop the maximum physical properties in the alloy. I have found that when alloys of the above composition are given my improved heat treatment, for example heating at 530 C. for about two hours, quenching, and then reheating from ten to twenty hours at 155 C., the physical properties of the alloys are greatly improved.

Alloys consisting of 5% silicon, 0.5% magnesium, 1.3% copper and 93.2% aluminum, when heat treated in accordance with the prior process, have the following properties:

Proportional limit pounds per square inch- 14,500 Tensile strength do. v 38,200 Elongation per cent The same alloys-when heat treated in accordance with my improved process, have the following properties:

Proportional limit pounds per square inch 22,500 Tensile strength ..,do.. 43,100 Elongation -..per cent 3.5-4.5

What I claim as new and desire to secure by Letters Patent of the United States, is: g

1. The method of heat treating aluminum base alloys containing about 7% silicon, about 0.3% magnesium and the remainder substantially aluminum which comprises heating the alloy at a temperature of 530 C. for about two hours, quenching and reheatingat 155 C. for at least ten hours.

2. The method of heat treating aluminum base alloys containing about 5% silicon, about 0.5% magnesium, about 1.3% copper and the remainder substantially aluminum, which comprises heating the alloy at a temperature of 530 C. for about two hours, quenching and reheating a 155 C. for at leastten hours.

RICHARDS n. mama-Ion. 

